1. Field of the Invention
The invention relates to methods and tools used in knee arthroplasty. More particularly, the invention relates to methods and tools used in total knee surgery (primary and revision applications) where an artificial femoral component is installed.
2. Brief Description of the Prior Art
Total knee arthroplasty involves the replacement of portions of the patella, femur and tibia with artificial components. In particular, a proximal portion of the tibia and a distal portion of the femur are cut away (resected) and replaced with artificial components. As used herein, when referring to bones or other body parts, the term xe2x80x9cproximalxe2x80x9d means closest to the heart and the term xe2x80x9cdistalxe2x80x9d means more distant from the heart. When referring to tools and instruments, the term xe2x80x9cproximalxe2x80x9d means closest to the practitioner and the term xe2x80x9cdistalxe2x80x9d means distant from the practitioner.
There are several types of knee prostheses known in the art. One type is sometimes referred to as a xe2x80x9cresurfacing typexe2x80x9d. In these prostheses, the articular surface of the distal femur and proximal tibia are xe2x80x9cresurfacedxe2x80x9d and replaced with respective metal and plastic condylar-type articular bearing components.
The femoral component is a metallic alloy construction (cobalt-chrome alloy or 6A14V titanium alloy) and provides medial and lateral condylar bearing surfaces of multi-radius design of similar shape and geometry as the natural distal femur or femoral-side of the knee joint.
Prior art FIG. 1 is a sectional view of a state of the art femoral component. The interior of the component has five planar fixation surfaces 1-5 and an intramedullary (xe2x80x9cIMxe2x80x9d) stem 6. Prior to installation of the component, the distal femur must be prepared so that it has five fixation surfaces which closely match the interior surfaces of the component and in scenarios where additional stability is desired the IM canal is reamed to accept the IM stem of the component.
More particularly, the distal femur must be resected to have a distal cut surface (corresponding to surface 1 in FIG. 1), a posterior cut surface (corresponding to surface 2 in FIG. 1), an anterior cut surface (corresponding to surface 3 in FIG. 1), an anterior chamfer cut surface (corresponding to surface 4 in FIG. 1) and a posterior chamfer cut surface (corresponding to surface 5 in FIG. 1). These cuts are typically made with oscillating saw blades.
A number of different devices can be used to control the positioning of the saw blades. Flat metallic blocks on which the saw blade is rested, obviously rely to some extent on the skill of the surgeon to avoid tilting of the saw blade, as may happen when the saw encounters a localized harder (sclerotic) section of bone, or when the saw blade has a long travel beyond the guide surface. Slots having small clearance relative to the thickness of the saw blade may also be used. In general these offer better control of the saw blade than open style blocks.
Block type cutting guides are shown in U.S. Pat. Nos. 4,474,177, 4,487,203, 4,502,483, 4,524,766 and 4,567,885.
Fulcrum type cutting guides are described in U.S. Pat. No. 4,718,413 and also in U.S. Pat. No. 4,892,093. These consist of an upper and a lower guide surface which are linearly separated along the plane of intended cut by the saw blade. By providing a separation between the two surfaces the saw blade, including its tooth set, may be introduced between the two surfaces and then biased against them to control the cutting plane.
The separation of the guide surfaces normal to the plane of operation of the saw blade is typically matched to the thickness of the saw blade. The choice of orientation of the guide surfaces is chosen so that any deviation by the surgeon in maintenance of the contact between the saw blades and either of the guide surfaces results in conservative removal of bone, which may be subsequently corrected. The guide of U.S. Pat. No. 4,892,093 sits on the already prepared distal femur and provides for the cutting of four additional cuts.
The femoral components may be located with six degrees of freedom relative to the patient""s femoral geometry. These can be expressed in a Cartesian manner relative to orthogonal anatomical reference planes as shown in FIG. 2. Angulation: Varus-Valgus, Flexion-Extension and Internal-External Rotation. Linear Position: Inferior-Superior, Anterior-Posterior and Medial-Lateral. To position the component on the bone, a number of datum features of the patients anatomy and their relative location as controlled by soft tissue structures at the knee may be utilized.
Two major schools of thought exist as to the optimum method to provide consistent functional placement. The first is independent femoral anatomical placement. In this technique the femoral component is positioned on the femur by referencing datum features on the femur itself. The second is referenced to the tibial position. In this technique the position of the femoral component is controlled relative to the proximal cut of the tibia. The ligaments and other soft tissue structures at the knee joint will in this case affect the femoral component""s position. The positional referencing, according to different methodologies, is performed surgically prior to placing the femoral component.
A third technique is varus-valgus and flexion-extension. Angulation of the component in planes is usually performed simultaneously. The reference datum is either the femoral shaft or the line joining the center of the knee and the hip joints. Two major techniques for accomplishing this are currently used. First is intramedullary alignment. A rod is introduced through the center of the knee into the intramedullary space and passed up the inside of the femur to the internal isthmus, establishing an instrument axis within the femoral shaft (medullary canal of the femur). This technique has been found to be very reliable. The second is extramedullary alignment. An external guide rod is aligned with the anterior cortex of the femur, or from the center of the knee to the femoral head.
Current techniques generally require the sequential use of alignment and cutting guides. In most current systems multiple cutting guides are needed to fully prepare the distal femur for the implant. Because these sequential operations require the assembly and disassembly of instrument configurations and the use of intermediate data cut onto the bone, there are penalties in terms of time of surgery and accuracy.
U.S. Pat. No. 5,454,816 discloses an orthopedic instrument for guiding a saw blade for shaping the distal end of a human femur to receive an endoprosthetic femoral component. The instrument includes a base component provided with a guide for guiding cutting elements for shaping all of the necessary surfaces to receive the femoral component to be fitted once the base component is fitted to the bone. Also included are alignment elements for aligning the base component on the bone and elements for attaching the base component to the bone after alignment.
All of the prior art cutting guides have certain drawbacks. These include the inability to provide accurate cuts on a variety of different size femurs, inability to accurately align with one or more of the femoral axes, difficulty in fixation of the guide to the femur, inability to make adjustments in positioning after alignment tools are removed, impingement of soft tissue when securing the cutting guide, etc.
It is therefore an object of the invention to provide methods and tools for performing femoral resection.
It is also an object of the invention to provide tools for performing femoral resection which maintain proper alignment while multiple resection cuts are made.
It is another object of the invention to provide methods for performing femoral resection in which a minimum number of tools are used.
It is still another object of the invention to provide methods and tools which enhance the accuracy of femoral resection.
It is also an object of the invention to provide methods and tools for performing femoral resection on a variety of different size femurs.
It is another object of the invention to provide methods and tools for performing femoral resection which allow for intraoperative adjustment of the cutting guide position.
It is still another object of the invention to provide tools for performing femoral resection which are easy to attach to the femur with minimal soft tissue impingement.
In accordance with these objects which will be discussed in detail below, the invention contemplates a tool set, including a plurality of different size cutting blocks (also referred to herein as xe2x80x9ccutting guidesxe2x80x9d); and methods for resecting the distal femur prior to implanting a prosthetic femoral component.
The cutting guides of the present invention, according to preferred embodiments thereof, each include (a) a block having a plurality of guiding surfaces, the plurality of guiding surfaces including (al) an anterior cutting guide surface for resecting the anterior cortex of the femur; (a2) a posterior cutting guide surface for resecting the posterior condyles; (a3) an anterior chamfer cutting guide surface; (a4) a posterior chamfer cutting guide surface; (a5) a distal cutting guide surface for resecting the distal end of the femur; and (b) means for securing the block to the distal femur.
The femoral resection tools of the present invention include a posterior condyle alignment guide, an IM rod with an adjustable valgus bushing assembly, zero, three, and five degree, left and right external rotation plates, an anterior sizing boom having a stylus and a pair of medial/lateral drill guides, a plurality of self-tapping screws, 0 mm, 2 mm and 4 mm proximal positioning fixtures with optional 2mm anterior and posterior positioning fixtures, and a plurality of different size cutting guide blocks (the aforementioned xe2x80x9ccutting guidesxe2x80x9d), each adapted to fit over the proximal positioning fixtures.
As indicated hereinabove, the cutting guide blocks contemplated by the preferred embodiment of the invention, provide three point cutting blade contact for guiding the anterior resection, posterior resection, posterior chamfer, anterior chamfer, and distal resection.
According to the methods of the invention, the valgus bushing is attached to the appropriate external rotation guide plate and both are attached to the posterior condyle alignment guide. An access hole is drilled into the IM canal. The IM rod is inserted through the valgus bushing and in the IM canal so that the assembly rests against the distal and posterior surfaces of the femur.
The assembly is locked securely into position and the anterior sizing boom is attached to the assembly. The stylus of the sizing boom is moved into position over the anterior femur and a size is indicated by indicia on a vertical post of the sizing boom.
The medial/lateral drill guides are moved against the medial and lateral sides of the femur and one or two fixation pins (self-tapping screws), depending on desired stability, are inserted through the holes in each drill guide. The drill guides, sizing boom, and alignment assembly are all removed leaving only the four fixation pins.
A pair of proximal positioning fixtures are selected and slid onto the fixation pins.
According to an alternate embodiment of the invention a pair of modular positioning fixtures can be detachably attached to the extension arms ahead of time to form an integrated drill guide assembly. According to the alternate embodiment of the invention, the need to select and slide a pair of positioning fixtures onto the fixation pins would be eliminated.
An appropriately sized cutting block is selected, based on the size indicated by the sizing boom, and is slid onto the proximal positioning fixtures. Additional fixation pins may then used to secure the position of the cutting block.
With the cutting block in place, five resections may be performed preferably in the following order: anterior resection, posterior resection, posterior chamfer, anterior chamfer, and distal resection. The rational behind this sequence is to allow the surgeon the ability to change the size and/or position of the femur immediately following the resection of the anterior femur.
The methods and tools of the invention provide for a wide range of alignment and sizing of the cutting guides described herein.
The cutting guides contemplated by the invention provide for very accurate cuts. The proximal positioning fixtures allow for 0 mm, 2 mm, or 4 mm distal offset and further, according to a presently preferred embodiment, also optionally permits +/xe2x88x922 mm anterior/posterior offset to correct any mistakes made in the initial sizing of the femur. The cutting blocks contemplated by the invention also allow for medial-lateral positioning. All of these positioning steps can be carried out between cuts thereby allowing intraoperative adjustment of the position of a cutting block.
The invention provides all of the advantages of anterior referencing without the disadvantage of flexion gap anterior-posterior sizing mismatch.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.